MXPA03007031A - Control system with capacitive detector. - Google Patents

Abstract

A capacitive sensor system for controlling operation of a device in response to a rate of change in capacitance due to motion of a proximate object includes at least two sense electrodes disposed on a surface and a phase locked loop, including a voltage controlled oscillator and a phase/frequency comparator, connected between the sense electrodes and an RC network for providing an operating frequency to the sense electrodes. A circuit loop, including a reference oscillator, provides a fixed frequency references for the phase locked loop to follow and a phase delay circuit connected between said phase/frequency comparator and said voltage controlled oscillator causes the voltage controlled oscillation to run ahead of the reference oscillator. A trigger circuit provides a control output in response to a change in phase shift frequency and said operating frequency.

Description

CONTROL SYSTEM WITH CAPACITIVE DETECTOR DESCRIPTIVE MEMORY The present invention relates generally to automatic control systems and relates more particularly to a system for the control operation of a device using a capacitive detector. Up to now, a large number of capacitive detectors have been developed to detect people or metals and provide an alarm, an indication signal or a control. For example, capacitive detector circuits have been used in alarm systems to provide a signal in response to contact with a particular area or the proximity of an object. In other examples, capacitive detector circuits have been used to detect the presence or absence of liquids and solids, and to then initiate an indicator for alarm or measurement signals. Capacitive detectors, have also been used to measure the distance of an object, the size of a material, the moisture content of a material, oil contamination, moisture, pressure, fluid level, and even have formed the basis of detection in numerous measurement and detection applications. With respect to the control of a dispenser, it is often preferred that the operation of a device be without direct manipulation thereof by human interaction. For example, it is preferably, for sanitary reasons in washing, to avoid the need for physical contact with tap faucets, towel dispensers, hand dryers, soap dispensers and the like. Although a number of control systems have been developed for such contact-free devices, to conserve water and soap, they have the problem of false activation. That is, devices are activated without the true presence of a part of the human body. Of course, this leads to waste of the fluid, which is contrary to the original purpose of the control system. In addition, in the case of soap dispensers and the like, safety becomes an important factor when said liquids are falsely dispensed and accumulate in the soil, or on another surface, where subsequent slippage in them can cause bodily harm. . The problem of false activation, and more generally that of the reliable and at the same time sensitive sensing of a nearby object by a proximity system, arises from the need for reliable discrimination between a small change in signal strength due to changes in the proximity of the object, against changes in signal strength that may occur as a result of other factors such as detector noise, detector drift, or changes induced in the signal due to true changes in the same environment, such as detector contamination and other effects that may result in signals that are similar in magnitude to, or even greater than, the same detection signal. In the case of infrared proximity detectors, which are frequently used, for example, in current non-contact soap dispensers and in other similar devices, false activation may arise due to scattering effects, light impact strange in the detector due to spurious reflections in the lustrous objects, or a failure in the detection of an object due to variations in the reflectivity of the object or the contamination of the optics may occur. In the case of capacitive proximity detectors, where an object is detected by means of detecting a change in capacitance due to the close presence of the object, it becomes difficult and unreliable to detect sensitive objects close to everyday environments , since true changes in capacitance due to a nearby object may be small compared to other changes in capacitance that are due to changes in the surroundings. Certain variations that commonly occur in the environment, which can cause such interference variations in the capacitance, include contamination of the surface of the electrodes or other structures in the region of the detection field by the gradual accumulation of dirt or condensed moisture, significant changes in the humidity of the environment, gradual variations in the proximity or composition of other structures of nearby objects, or variations in the mounting location of the detector, all this can give rise to small alterations in the shape or intensity of the electric field between the electrodes of the detector, thus altering the state of the load and therefore the capacitance between the electrodes. Currently there are two basic types of capacitive proximity detector in the prior art known. In one case, which is commonly called the type of parallel plate, there is only one sensor electrode in the detector and the capacitance to ground is measured. If the object to be detected is generally conductive and is connected to ground, it can effectively form the second electrode, such that the movement of the object towards or away from the main sensor electrode changes the capacitance, and this change is measured and relates to the distance or proximity of the object. If the object to be detected is not electrically conductive, a second stationary electrode is incorporated at a fixed distance and connected to ground, and the object to be detected passes between the two electrodes resulting in a change in capacitance. In the second case, which is known as the marginal field type, there are two sensor electrodes that are arranged close to each other in the detector, and the object that will be detected changes the capacitance between them, changing the field electrical using dielectric or conductive effects. The resulting change in capacitance is detected and can then be related to a change in the distance or proximity of the object. Capacitive proximity type proximity field type detectors are widely used in industry, in manufacturing applications where sensing facilities are typically specified and fixed, and other environmental factors can be controlled with potential interference. However, such devices often also incorporate an additional electrode to detect separately and thereby compensate for the deviation due to surface contamination. The maximum detection distance is the scale of the detector and is related to the sensitivity of the capacitance change detection technique, to the nature and size of the object to be detected and to the physical size of the sensing electrodes. The larger sensor electrodes provide a larger scale. A greater sensitive detection provides a larger scale with a given size of electrodes and a given object that will be detected, which is an advantage of operation in applications where larger electrode structures are not desirable, and in those that do. you want a larger scale. However, the most sensitive detection of changes in capacitance does not in itself provide reliability, where significant changes in capacitance may also arise due to environmental factors. The present invention was developed to overcome the drawbacks of the systems known up to now, to provide a capacitive detector system with improved sensitivity and reliability.

This is achieved by providing sensitive means to detect only the change ratio of the capacitance. This amount is mathematically denoted as dC / dt and is distinctly different from a measurement of the difference between two capacitances, as is typical in the prior art.

DC = the ratio of capacitance change with respect to time Dt Therefore this is contrary to systems known from the prior art, in which the detection is based on a change in capacitance. In the present invention, the detection, which is performed in the phase domain using a continuously operating control loop, is therefore advantageously insensitive to gradual changes. in the capacitance that are due to changes in the environment, which can be of any absolute magnitude, as long as these changes occur in sufficient lengths of time and therefore at ratios that are below the detection sensitivity for the dC / dt. It will be appreciated that although a time relation of the change signal could in principle be derived alternatively from the output of several capacitive sensors of the prior art, by measuring the capacitance change, by electronic differentiation of the signal, said derived signal it would not then provide the reliable and sensitive detection that is required. This is because the simple act of differentiating a detector signal makes the resulting signal louder and therefore less reliable. In the present invention, a capacitive sensing means is provided that is intrinsically responsive to movement to detect the movement of an object, for example the hand of a person, in a region that lies within a prescribed range of distance of the detector. The system according to the present invention provides a means to reliably detect the small movements of a hand towards the detector, when it is within the detection region. Furthermore, accounting is independent of whether the person is electrically grounded or not, or even if it is intermittently connected to ground during the detection operation, as may occur in the case of someone who is washing their hands. This reliability inherently provides an immunity to false activation, since the detector continuously adapts to the electrical characteristics of the surroundings and to the gradual changes in those surroundings that are of a general magnitude greater than that which is due to the introduction of a hand in the detection region. In this way the detector has a derivation of 0. Thus, the present invention is functional on a scale of different surroundings, without the need for manual adjustment. In addition, the present invention is highly immune to RF and other externally generated electric field interferences, has low electromagnetic emissions per se and consumes little energy. This last characteristic makes possible the prolonged operation by means of a battery.

BRIEF DESCRIPTION OF THE INVENTION A capacitive detector system according to the present invention for controlling the operation of a device in response to the ratio of the change in capacitance due to the movement of a nearby object, generally comprises at least two sensing electrodes which are arranged in a separate relationship to enable the establishment of an electric field between the sensor electrodes. An electronic circuit provides a control output signal in response to a ratio of the change in capacitance of the sensing electrodes due to the movement of the proximal object within the field, without an intermediate electronic differentiation of the signals related to a change in capacitance. Preferably, the sensor electrodes are arranged on a flat surface, and in this configuration, makes it possible to establish an electric field that extends outwards between the sensing electrodes. More particularly, the electronic circuit may include a frequency control loop for phase lock (PLL) that includes a controlled voltage oscillator (VCO), a fixed frequency reference oscillator for the VCO to follow, a phase comparator. / frequency, a phase delay network to delay the phase of the VCO output with respect to the reference one and which acts to cause the VCO frequency to run in front of the reference oscillator when the loop is in phase latch and a loop filter that integrates the phase error signal from the comparator and thus defines the dynamic response of the loop. The characteristics of the loop filter are such that they diminish and even match the dynamic response of the loop to the time scale characteristic of the movement of the object to be detected. In addition, a phase-sensitive activating circuit is connected between the VCO and the reference oscillator and generates the output signal of the detector each time these two signals are in phase. The VCO is connected to the sensor electrodes in such a way that any increase in capacitance in them acts to decrease the frequency of the VCO and vice versa. A capacitance change caused by an object moving in the detection region of the sensing electrodes causes a phase switching at the operating frequency with respect to the reference frequency which is larger for the larger ratios of change in the capacitance of the capacitor. the sensor electrodes. The phase error signal that is generated in this way by the comparator is integrated in the filter of the circuit and if the phase error accumulates in a sufficiently fast relation, in such a way that the phase switching exceeds the defined threshold by the phase delay network, then an output or drive signal of the detector is generated. This signal can then be used to control another device, such as a soap pump where the detector is used to detect the movement of the hand near a non-contact soap dispenser, or an indication of proximity by means of the connection to a deployment device or alarm. In the preferred embodiment of the present invention the generating circuit of the driving signal includes a delay jog circuit and in an alternative embodiment the driving circuit includes a voltage comparator. In the preferred embodiment, a frequency divider is included between the VCO and the phase / frequency comparator, which causes the frequency of the VCO to operate at a frequency that is a fixed multiple to that of the reference oscillator. Also, in the preferred embodiment of the present invention, the control loop incorporates an additional feedback path for the circuit that is parallel to the loop filter and serves to eliminate the multiple trigger signals for phase delay errors that are very large , which could be caused by very large dC / dt generated in the sensor electrodes. This feedback path incorporates a circuit that can be adapted to very large phase error signals in such a way that for small error signals it provides negligible output while for very large signals it does not allow the phase difference to move out the scale of +/- 90 degrees. In the preferred embodiment, this feedback path incorporates iods together with an RC demodulator network. More particularly, the VCO provides an operating frequency to the sensing electrodes that is high enough to ensure that if the object is a human hand and if the individual is grounded, that despite this the hand is detected as an object. dielectric. This eliminates any possible detection artifact due to variations in the electrical ground connection of the hand and, as already known in the prior art, places a minimum requirement of operation frequency in the detector of a few thousand kilohertz. Therefore in the preferred embodiment and if the object is a hand and the device is a soap dispenser, the operating frequency is set at approximately 0.5 MHz. Taking this into account and as an alternative for other detection applications, the purpose of avoiding driving effects may impose other preferred restrictions on the frequency of operation. Said restrictions are within the scope of the invention. Preferably, an electrode with shield connected to ground is also provided and is disposed in a separate parallel and above relationship to these sensor electrodes. This eliminates the electric detection field in the region above the shield so that this region can be used without falsely activating the system. In an alternative mode the shielded electrode can be divided into two halves and each half can be driven at the same voltage as the opposite sensing electrode in order to reduce the capacitance between the sensing electrodes and the shield, and with this the sensitivity and therefore both the detection scale. This alternative requires additional electronic circuits to generate the voltage waveform for the shield.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention will be better understood by the following description when considered together with the accompanying drawings in which: Figure 1 is a block diagram of an embodiment of the present invention, wherein the activator uses a delay jog circuit; Figure 2 is a diagram of the circuits that appear in the block diagram of Figure 1; Figure 3 is a block diagram of an alternative embodiment of the present invention, wherein a comparator is used for the activator; Fig. 4 is a drawing of a sensor electrode configuration that is suitable for use with the block diagram as shown in Figs. 1 or 3; and Figure 5 is a graph of the change measured in the capacitance of the sensor electrodes that appear in Figure 4, due to the presence of a pest. DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1 a block diagram of the electronic parts of the detector 10 according to the present invention is shown. The circuit shown is an example of electronic circuits for providing a control output signal in response to a change in the capacitance of the sensor electrodes due to the movement of the next object within the field, without an intermediate electronic differentiation of the signals related to a change in capacitance. The general principle of operation is as follows: a phase-locked frequency control loop (PLL) 12 is interconnected with the sensor electrodes 14 and 16. The PLL includes a controlled voltage oscillator (VCO) 22 having an output, whose frequency is linearly related to the input control voltage 102. The output is connected to a phase / frequency comparator by means of a frequency divider 100 and a fixed phase delay network 34. A reference oscillator 32 is also connected. to the comparator and generates a continuous fixed frequency signal. The phase / frequency comparator 24 generally provides a high voltage (Vcc) if the divided frequency of the VCO is lower than the reference frequency, and a low voltage (0) if the divided frequency of the VCO is higher than the reference frequency. Furthermore, when the two frequencies are equal but there is a phase difference between them, the comparator 24 detects the high edges of the two signals and generates a pulse output, whose width is proportional to that of the phase difference where it is. between 7- 360 degrees. The average circuit control voltage is activated between 0 and Vcc in a linear fashion, with the general result that the phase / frequency comparator has the tendency to activate the high edges of the two signals presented to it at a phase difference zero. When this is achieved the PLL sets the phase such that the phase of the divided frequency of the VCO is always ahead of the reference frequency by the amount defined by the phase delay network 34. This is the normal state of rest of the detector. In the preferred embodiment, the frequency divider 100 divides the VCO frequency by 16 so that the VCO operates 16 times the frequency of the reference oscillator. By using a frequency divider in this way, it allows the use of a lower inexpensive frequency, low energy, the reference oscillator and is not essential for the basic operation of the detector. The VCO and the phase / frequency comparator can be, for example, elements of a CD74HC4046AM chip manufactured by Texas Instruments. The loop filter 20 is an RC network and incorporates a large capacitor that dominates the dynamic response of the control loop. A small resistor is placed in series with this capacitance and connected to the VCO 102 input. This resistor allows the control loop to energize a small amount of the circuit noise and thus stabilize the phase relationship between the VCO and the reference signals.

An additional feedback path 101 is also preferably included, which is connected in parallel with the loop filter 20. This serves to eliminate the false multi-drive signals that would otherwise occur in examples or in applications where it is sometimes they generate very large phase delay errors due to the very large dC / dt 'that occur in the sensor electrodes. Such large signals could occur in applications where there could be a usually rapid movement of the object to be detected or by movements of that object on a nearby scale. Such examples of occasional large signals could occur if -the detector is used to detect the movement of the hands in a soap dispenser application. This feedback path incorporates a circuit that can be adapted to very large phase error signals, so that for small error signals it provides an insignificant output, while for very large signals it does not allow the phase difference to be move off the scale of +/- 90 degrees. In the preferred embodiment, the parallel feedback path incorporates two diodes in series in the direction of phase switching, which causes an activation and a diode in the opposite direction together with an RC demodulator circuit. This provides an alternative parallel feedback path to which the phase error signal can not over-energize.

A sensitive phase comparator, such as a D-type jogger 30, is connected to the reference oscillator 32 and the frequency divided VCO signal where the reference is connected to the data input and the VCO is connected to the input of the clock. This device is used as an activator to generate the output signal of the detector. The capacitance increases in the sensor electrodes due to the movement of an object, such as a hand (does not appear), in the activation region and where this is done at a sufficient speed to energize the circuit, the phase between these signals will have the tendency to be switched. Each time this switch is equal to or exceeds the phase threshold set by the phase delay network 34, the data input will be lower and not high at the time of the clock transition and an output pulse will be generated. activation. It can be seen that the arrangement described above is configured to detect only positive dC / dt as opposed to negative dC / dt, or dC / dt positive and negative. This means that the detector configuration described above only generates an output when the object to be detected moves towards the sensing electrodes instead of away from the sensing electrodes. This mode of operation is by design and is specifically advantageous in a soap dispenser application, where it is preferable that the soap be dispensed only when a hand is moved towards the dispenser, and not when the hand is being moved away from the dispenser. This mode of operation is appropriate for its simplicity and the intuitive ease of use by typical users of a soap dispenser, and also confers an additional and advantageous performance characteristic that is specific to a soap dispenser application. This additional feature is applied in the case where a user requires an additional or consecutive soap assortment, which therefore requires additional or consecutive generations of the detector activating signals. In this case, and because the detector is sensitive to positive dC / dt, and conforms to static changes in capacitance, due for example to changes induced by the static presence of a hand, the user does not need to withdraw by complete your hand and reinsert it into the detection region, and you can simply advance your hand towards the sensing electrodes, or you can alternatively move your hands up and down in small movements within the activation region, with what will happen the activation of the detector and the assortment of soap with the detection of each movement towards the sensor electrodes. If it is required and if it is advantageous for other applications, the detector circuit could easily be configured to detect negative dC / dt events, where the activating signal would be generated if the object to be detected moves out of and away from the region of activation, instead of inside and towards it. Said detector could be used in principle in applications where it is preferable to detect the movement of an object that moves outwards, or that is being removed from within a region.

The rest phase relationship can be set in one of several ways, but it is preferable to build a phase delay element 34 using a small RC network at the phase input and the frequency comparator 24. This makes the oscillator of the VCO 22 operates ahead of the reference oscillator 32 by an amount that will be balanced between the need for noise immunity and the need for sensitivity. The closer the phases work, the trigger circuit will be more sensitive. The larger the phase switching between them, the greater the noise tolerance of the circuit, and the instability of the oscillator. This element 34 establishes the activation threshold. In the case where the frequency of the reference oscillator is about 32 kHz, the phase delay can be set to a value on the scale of 0.5 to 4 s, which is equivalent to approximately 6 to 45 degrees and is set to preference to a 1.5 s delay. With respect to RF interference, it is known that typical capacitive sensors of the prior art are often vulnerable to false activation due to the effects of electromagnetic scattering radiation. In the present invention a high degree of immunity to RF interferences of this type is presented due to the fact that the detector is based on a PLL circuit which is tuned, or which operates at a specific and low frequency, and which, therefore, it has a good inherent rejection of the frequencies that are above and below this frequency.

However, in spurious application environments, RF can occur, which is sufficiently intense and at sufficient frequencies to falsely drive the detector. In view of this, in the preferred embodiment the filters 103 and 104 are connected between the sensor electrodes and the VCO 22. These filters reduce the magnitude of the intrusion in the detector circuit of high frequency signals due to dispersion or interference of strange and spurious RF, which can be irradiated, for example, by kitchen appliances such as microwave ovens, and also by cell phones, and which could have a sufficient intensity to induce the false activation of the detector. These filters may contain ferrite filters, however in the case of the soap dispenser application, sufficient attenuation can be achieved using a simple network of resistors and capacitors. Figure 2 is a schematic diagram of a practical detector circuit 10 in which the two sensor electrodes are connected directly to the points denoted by J1 and J2. In particular, this circuit also includes a supply for the use of a shielded electrode, in which the shielded electrode is directly connected to the connection point denoted by J3. Those skilled in the art can easily construct this circuit on a printed circuit board, using the components indicated in figure 2. It will also be appreciated that if desired for reasons concerning the economy of mass production in large volumes, the circuit it could be further refined and provided in a single integrated circuit electronic component known as a specific application integrated circuit (ASIC) by those skilled in the art. The following mathematical representation of the detector's dynamic response is provided to better explain and illustrate the basic operation of the detector. The response of circuit 10 will be different for the different forms of capacitance change over time. For the application of for the application of the soap dispenser a reasonable approximation to this form is a change of ramp in the capacitance. Therefore, the solution to the analysis of the response of the circuit, where the activating circuit is based on a tilter D and for a change of ramp in capacitance, is provided by: where where: Ko = Gain constant F1 = The operating frequency of the VCO corresponding to the control voltage V1 of the VCO. F2 = The operating frequency of the VCO corresponding to the voltage control of the VCO. In practice, and depending on the precise characteristics of the specific device or devices used, the gain constant, Ko as expressed in the above equation, is not an exactly linear function of the frequency and control voltage. However, it is typically approximately linear over a certain scale of values. Also for the purpose of the design, in general Ko is a non-linear function of a scale of circuit parameters that can be expressed in a general way by: KO = F Vcc, N,?, R \, R2, C) Where: Vcc = the supply voltage y is equal to 3.3V = in the circuit represented in figure 2. N = number of times in which the VCO frequency is divided due to the circuit element 100? = the circular frequency of the reference oscillator 32.

R1 = corresponding resistance value in the circuit diagram illustrated in Figure 2 to R1 R2 = corresponding resistance value in the circuit diagram illustrated in Figure 2 to R2, and wherein the precise functional relationship required for design purposes of The circuit, denoted by F in the above equation, can be determined from the detailed data presented in the supplier data sheets, which, for example, are graphically presented in a variety of ways on "CD54 / 74HC4046A Texas Instruments Data Sheet, Feb. 1998 revised May 2000. ", which describes the operation of the particular PLL circuit element illustrated in Figure 2. VCO = the middle part of the control voltage scale 102, ie Vcc / 2, where Vcc is the supply voltage and is equal to 3.3V in the circuit illustrated in Figure 2) Vref = reference voltage which is internal to the PLL chip.

Vcc Kd = ^ wherein: R3, R4 and C are the components of the loop filter (corresponding to the circuit diagram illustrated in Fig. 2 to R9, R8 and the capacitance C7). t = time? = \ 3 damping ratio that is provided by: where t2 = R4.C The equation shown above has a main term, which multiplies a time-dependent response term. This last term is eventually reduced to 0. The magnitude of the initial response, which generates the activation, is therefore proportional to the main term and as such can be seen to be proportional to the change ratio of the capacitance divided by the total capacitance. The initial response is also inversely proportional to the natural frequency of the loop circuit, which indicates, as might be expected, that the response is greater for the circuits that are corrected more slowly. Figure 3 illustrates a block diagram of the sensor electronics 40 in accordance with an alternate embodiment of the present invention and includes common reference numbers illustrating identical or subsequently similar elements described with respect to the embodiment 10 shown in FIG. Figure 1. In this mode 40, the trigger is based on a voltage comparator 42. This is an alternative detection method and uses the control circuit of the phase synchronization loop (PLL) 12. The operation is as follows: same as in > the mode 10 shown in Figure 1, the average control voltage is the voltage required to cause the VCP 22 to operate at the same frequency, after division, as the reference oscillator 32. However, in this mode there is no phase delay network and conversely the phase change errors will cause the phase / frequency comparator 24 to increase or decrease the control voltage 102 until the difference in phase is corrected to 0. In this arrangement 40 , the phase error signal of the frequency / phase comparator 24 is filtered by a first loop filter which may comprise an RC44 network and is also filtered by a second filter, which may also comprise an RC105 network and which has a much longer time constant than the first RC network and which provides a voltage reference to the comparator 42. When the control voltage 102 reaches a voltage threshold in the positive direction predetermined in the comparator 42, due to the detection of a moving object within the activation region of the sensor electrodes 14 and 16, the comparator 42 is activated and provides the output signal of the sensor.

Operating frequency The operating frequency of the sensor for a soap dispenser (not shown) is the VCO frequency and is approximately 0.5 MHz (the true frequency is 16 times the reference oscillator frequency of 32,768 KHz which equals 0.5244 MHz). This frequency is adjusted to be high enough so that a person's hand is always detected by the sensor, sometimes as a dielectric material when a conductor is contracted, and as a dielectric material in others that could generate variability in the activation scale and in general performance. This aspect arises due to the fact that an individual operating the jet may or may not be electrically grounded. For example, the operator, when requesting soap, may sometimes have a hand in contact with a metallic object to ground such as a sink or faucet, or be electrically connected to ground by the flow of running water. In order for the person's hand to be detected as dielectric, the frequency needs to exceed the free charge relaxation time of the human body. This time is determined from the product of the resistance of the skin to the earth in ohms and the capacitance of the body in farad. The capacitance of an adult human is in the region of 50pF. The resistance of the skin between two hands varies somewhat in the region of about 100 k to a few. Therefore, the RC time constant can be as little as 5 s, which corresponds to a frequency of 0.2 MHz. Therefore, the operating frequency of 0.5 MHz was selected to provide a reasonable margin. Other potential applications include the control of faucets. The effective use of capacitance sensors for the control of faucets perhaps requires significantly higher frequencies in the region of 10 MHz or greater. This is noted in the patent 5,730,165 and is generally documented in others. The reasoning is again based on the contents of RC time and has to do with the greater conductivity present in a washroom environment. There is no fundamental problem to modify the sensor design so that it operates at much higher frequencies if desired. In fact, with regard to the frequency of operation, the current state of the art in PLL devices covers even up to the GHz region. Thus, this design could be modified by "one skilled in the art" to operate in any desired frequency up to the GHz region in accordance with the needs of the intended application.

Figure 4 illustrates a simulated soap dispenser base 50 having the electrodes 14, 16 formed from copper foil, arranged in a separate relationship to allow the establishment of an electric field therebetween. This side-by-side arrangement generates an electric field between the two electrodes that extends outward from the electrode surfaces and curves between the two. The base 52 also incorporates a shielding electrode which in this example is formed from copper foil and wrapped around the outer side of the base 52. In this configuration, the magnitude of the field strength declines non-linearly with the distance from the electrodes, 14, 16, as well as the magnitude of change in capacitance due to the presence of a dielectric material within said field, such as a hand. This type of side-by-side configuration generates what can be called as a periphery field and the sensor in combination with this electrode configuration can be referred to as a type of capacitive sensor periphery field. As a basic guide, the intensity of the electric field typically descends rapidly in a periphery field at distances that exceed the combined width of the electrodes 14, 16, which in this case is about 7.62 cm. The extension from front to back is 7.87 cm; the extension from side to side is 8.25 cm; the separation is about 1.27 cm; The gap between the electrodes and the shielded flank is around 0.63 cm all around.

The change in capacitance was measured due to the presence of a hand at scales of different distances from the simulated base. Figure 5 shows the changes in capacitance for an adult hand, in an extended and flat manner on different vertical distance scales above the base 50 where a shield 52 was present and which was removed, which confirms this. There are two technical side effects for shielding connected to ground 52. The first is that it raises the overall capacitance of the sensor electrode structure by a few pF. The second is that it derives a portion of the electric field away from the sensitive region so that the capacitance changes on a fixed distance scale decrease. This can not be avoided for a shield connected to ground in close proximity to the sensor electrodes and is confirmed by the data shown in FIG. 5. Therefore, for this particular physical structure, the shielding requirement increases the required sensitivity of the shield. sensor and, as confirmed by the test data described herein, this sensor has the necessary sensitivity. If sensitivity were ever a problem for this or other applications requiring a similar shielded electrode, then an alternative arrangement that would require less sensitivity would be to split the shield and excite the two halves with the same voltage as the sensing electrodes.

Characterization of sensor and test data in the workshop The data fall into the following categories: • Characterization compared with known small capacitance change ratios. • Characterization compared with the response to the movement of the hand above the simulated base. Dynamic simulation and test data A test setup was constructed that was used for the characterization and as a means to generate a scale of known and reproducible capacitance changes in representative change ratios other than capacitance that occur during different time scales and that they are representative of the movement of the hand, and with capacitance change time profiles approaching a ramp. It is based on a parallel plate capacitor comprising two flat parallel electrodes, which are nominally square 5 cm by 5 cm and separated by a distance of 1 cm. Dielectric test samples comprising small squares of pure fused silica with dimensions of 0.93 square cm by 1 mm thick were used to progressively increase the capacitance. The material has a known dielectric constant of 3.8. The progressive increase in capacitance due to the introduction of said sample in the field region of the capacitor was calculated to be 6.3 fF, given the current precise dimensions of the structure and the test samples and assuming a uniform field. A means was created to introduce and withdraw the sample in and out of the field region at a known and constant rate. This included assembling the sample on a thin plastic disk that crosses the field gap and that rotates by means of a small electric motor with known RPs. This arrangement thus provides a means to simulate relationships of change and capacitance due to the movement of the hand. The following engine RPMs were used when the test sample was placed on the outer end edge of the plastic disc. Each rotation generates a positive dC / dt as the sample enters the field between the plates, as well as a negative dC / dt as the sample moves away from the field.

RPM?, Radians / s Speed, cm / s Event duration, ms DC / dt, fF / s 13.5 1.42 7.9 140 45 23 2.41 13.4 82 77 32 3.35 18.6 56 107 Since each rotation generates a dC / dt and a negative dC / dt, the arrangement also allows a test of sensors that activate the sensitivity with different magnitudes dC / dt and false activation with different -dC / dt. This is also useful since for the soap dispenser application, the sensor should not be activated due to the removal of the hand from within the activation region. The following data relates to approximately 100 revolutions in each speed: RPM Percentage of activation,% Percentage of false activation,% 13. 5 34 0 23 91 0 32 100 0 These data, taken in combination with those of the previous table, indicate that the sensor is sensitive to events that exceed +77 fF / s with a duration of 82 ms and is 100% successful (-1%) in these tests to detect events of +107 fF / s with a duration of 89 ms. The data also confirms that the sensor is able to reliably detect the movement of a small dielectric object other than a hand. The data also confirm that the sensor is functional when the sensor electrodes are arranged in a parallel plate type configuration.

Hand-held test data To provide further evidence of the reduction in the number of practices and application convenience in the context of activation of a contact-free soap dispenser, a series of manual activation tests were carried out using the base of the simulated soap dispenser incorporating the periphery field configuration of the sensor electrodes, as well as a shielded electrode as illustrated in Figure 4. Referring to Figure 5, the hand speed required for the reliable activation when approaching it vertically so that it activates the sensor in scales of 7.62, 5.08 and 2.54 cm. Later this technical calculation can be compared with real data for the same hand. The lower curve indicates a change in capacitance due to a hand on a scale of 7.62 cm from about 5fF, around 12fF to 5.08 cm and around 39fF to 7.62 cm. It can be calculated that this change will accumulate between an initial hand distance of about 12.7 cm and the activation distance of 7.62 cm, and so on. So that then the exchange ratio is around 100fF / s, the speed of the hand will have to be around 100 * 0.4 cm per second = 101.6 cm per second for activation at 7.62 cm (duration of 50 ms), about 100 * 0.16 cm per second = 43.18 cm per second for activation at 5.08 cm (120 ms) and around 100 * 0.05 = 12.7 cm per second for activation at 2.54 cm (444 ms). 12.7 cm per second is a very slow hand speed, while 63.5 to 101.6 cm per second may be more typical. The sensor circuit was connected to the simulated base and its activation was proved by a hand that moved towards the base in what was judged to be the normal speed and for repeated activation when the hand is already within the activation region, 10 times for each case.

Test: Hand moved from side to side within the activation region Scale, cm False Activations activ. 7.62 4 0 6.35 10 0 5.08 10 0 Test: Hand moved vertically in the activation region Scale, cm False activations activ. 7.62 4 0 6.35 8 0 5.08 10 0 Test: Hand moved from 0.75 to 2.54 cm vertically within the activation region Scale, cm Activations False activ. 10.16 3 0 8.89 6 0 7.62 10 0 6.35 10 0 It should be noted that the previous tests are technical or "between stages" in the sense that caution was taken to keep the hand extended and level, something that typical users of a soap dispenser would not do, in addition to the speed of the hand is a important factor and the above was based on the judgment of what would be typical and what would vary in actual use. It can be seen that according to these data, the effective activation distance is in the region of 6.35 to 7.62 cm and that this also agrees with the technical calculation. Similarly, it can be observed that there was a zero incidence of false activations, which means that at no time was the sensor activated by the withdrawal of the hand. The electric current draw for circuit 10 is low and substantially less than 1 mA with a low voltage. This demonstrates its suitability for long-term operation using alkaline batteries. The foregoing is advantageous for applications in devices powered by bacteria whose preferred purpose is for continuous operation for extended periods without the need to replace the batteries frequently. Although a control system according to the present invention has been described above for the purpose of illustrating the manner in which the invention can be used with convenience, it should be appreciated that the invention is not ted to the present. Likewise, each and every one of the modifications, variations or equivalent arrangements that occur to those skilled in the art, should be considered within the scope of the invention as defined by the appended claims.

Claims (24)

NOVELTY OF THE INVENTION CLAIMS

1. - A capacitive sensor system for controlling the operation of a device, and the system comprises: sensor electrodes to allow the establishment of an electric field to intercept the movement of a nearby object; and an electronic circuit for providing a control output signal in response to a change in capacitance ratio of the sensing electrodes due to the movement of the proximal object within the field without differentiation of related intermediate electronic signals: with a change in capacitance.

2. The system according to claim 1, further characterized in that said electronic circuit comprises: a phase synchronization loop, which includes a voltage controloscillator (VCO), connected to the sensor electrodes, to provide an operating frequency for the sensor electrodes; a fixed frequency reference oscillator to provide a fixed frequency reference; a phase / frequency comparator for comparing a VCO frequency with the fixed reference frequency; a phase delay circuit for changing a base difference between the VCO frequency and the frequency of the fixed reference oscillator when the loop is phase locked; a loop filter for integrating a phase error signal from the phase / frequency comparator to define a dynamic response of the loop; and a phase sensitive activation circuit for providing a control output signal in response to a change in a phase difference between the fixed reference frequency and the operating frequency.

3. The system according to claim 2, further characterized in that the phase delay circuit operates to cause the VCO frequency to operate in front of the fixed reference frequency so that a positive change in capacitance ratio controls the operation Of the device.

4. - The system according to claim 2, further characterized in that the phase delay circuit operates to cause the VCO frequency to function delayed at the fixed reference frequency so that a negative change ratio in the capacitance controls the operation of the device.

5. - A capacitive sensor system for controlling the operation of the device in response to a change in capacitance ratio due to the movement of a nearby object, and the system comprises: at least two sensing electrodes arranged in a separate relationship to allow the establishment of an electric field between the sensing electrodes, and said electric field extends outwardly and between the sensing electrodes; a phase synchronization loop, including a controlvoltage oscillator (VCO), connected to the sensing electrodes, to provide an operating frequency to the sensing electrodes; a fixed frequency reference oscillator to provide a fixed frequency reference; a phase / frequency comparator for comparing a VCO frequency with the fixed reference frequency; a phase delay circuit for changing a phase difference between the VCO frequency and the frequency of the fixed reference oscillator when the loop is phase locked; a loop filter for integrating a phase error signal from the phase / frequency comparator to define a dynamic response of the loop; and a phase sensitive activation circuit for providing a control output signal in response to a change in a phase difference between the fixed reference frequency and the operating frequency.

6. - The system according to claim 5, further characterized in that the phase delay circuit operates to cause the VCO frequency to operate ahead of the fixed reference frequency so that a positive change in capacitance ratio controls the operation Of the device.

7. - The system according to claim 5, further characterized in that the phase delay circuit operates to cause the VCO frequency to function delayed from the fixed reference frequency, so that a negative change in capacitance ratio controls the operation of the device.

8. - The system according to any of claims 5, 6 or 7, further characterized in that the controlled voltage oscillator provides an operating frequency to the sensing electrodes sufficiently high to ensure that the object is detected by the sensing electrodes as a dielectric material.

9. - The system according to claim 8, further characterized in that the controlled voltage oscillator provides an operating frequency of less than about 1 MHz to operate a soap dispenser by the movement of a human hand.

10. - The system according to claim 8, further characterized in that the controlled voltage oscillator provides an operating frequency greater than about 10 MHz to operate a tap by the movement of a human hand.

11. - The system according to claim 5, further characterized in that the electrodes are arranged in a planar relationship.

12. - The system according to claim 11, further characterized in that it also comprises a shielded electrode connected to ground arranged in a separate and surrounding relationship with the sensor electrodes, and the shielded electrode is in a plane generally perpendicular to the sensor electrodes and it extends away from the field of the established electrode.

13. The system according to claim 11, further characterized in that it also comprises a shielded electrode connected to ground disposed in a plane generally parallel to the sensor electrodes.

14. - The system according to claim 5, further characterized in that said activation circuit comprises a swivel type circuit D.

15. - A capacitive sensor system for controlling the operation of a device in response to a change in capacitance ratio due to movement of a proximal object, and the system comprises: at least two sensing electrodes arranged in a separate relationship to allow the establishment of an electric field between the sensing electrodes, said electric field extends outwardly and between the sensing electrodes; a phase synchronization loop, including a controlled voltage oscillator (VCO), connected to the sensing electrodes to provide an operating frequency to the sensing electrodes; a fixed frequency reference oscillator to provide a fixed frequency reference; a loop filter for integrating a phase error signal from the phase / frequency comparator to define a dynamic response of the loop; and a phase sensitive actrivator circuit for providing a control output signal in response to a change in a phase difference between the fixed reference frequency and the operating frequency, and the activating circuit includes a voltage comparator, which has a side connected to the VCO, and a constant loop filter for a long time connected between the phase / frequency comparator and the voltage comparator.

16. - A capacitive sensor system for controlling the operation of a device in response to a change in capacitance ratio due to the movement of a nearby object, and the system comprises: at least two sensing electrodes arranged in a separate relationship to allow the establishment of an electric field between the sensing electrodes; a phase synchronization loop, including a controlled voltage oscillator (VCO), connected to the sensing electrodes, to provide an operating frequency to the sensing electrodes; a fixed frequency reference oscillator to provide a fixed frequency reference; a phase / frequency comparator for comparing a VCO frequency with the fixed reference frequency; a circuit for phase delay connected between said phase / frequency comparator and said controlled voltage oscillator to cause said controlled voltage oscillator to operate in front of the reference oscillator; and an activating circuit for providing a control output in response to a variation in phase change between said fixed frequency and said operating frequency.

17. The system according to claim 16, further characterized in that the controlled voltage oscillator provides an operating frequency to the sensor electrodes high enough to ensure that the object is detected by the same electrodes as a dielectric material.

18. The system according to claim 17, further characterized in that the controlled voltage oscillator provides an operating frequency of less than about 1 MHz to operate a soap dispenser by the movement of a human hand.

19. - The system according to claim 17, further characterized in that the controlled voltage oscillator provides an operating frequency greater than about 10 MHz to operate a tap by human hand movement.

20. The system according to claim 19, further characterized in that it also comprises a shielded electrode arranged in a separate and surrounding relationship with the sensor electrodes.

21. - The system according to claim 16, further characterized in that said activator circuit comprises a tilting circuit D.

22. The system according to claim 5, 15 or 16, further characterized in that it also comprises an adaptive feedback path connected between the phase / frequency comparator and the VCO to maintain a phase difference between the fixed reference frequency and the VCO operating frequency between +90 and -90 degrees.

23. - The system according to claim 5, 15 or 16, further characterized in that it also comprises an RF attenuator filter interconnected between each VCO sensor electrode.

24. The system according to claim 5, 15 or 16, further characterized in that it also includes a frequency divider that interconnects the VCO and the phase / frequency comparator.